The present invention relates generally to the field of semiconductor devices, and more particularly to the formation of modified gate lengths.
The fabrication of semiconductor devices involves forming electronic components in and on semiconductor substrates, such as silicon wafers. These electronic components may include one or more conductive layers, one or more insulation layers, and doped regions formed by implanting various dopants into portions of a semiconductor substrate to achieve specific electrical properties. Semiconductor devices include transistors, resistors, capacitors, and the like, with intermediate and overlying metallization patterns at varying levels, separated by dielectric materials, which interconnect the semiconductor devices to form integrated circuits.
Field-effect transistors (FETs), such as metal-oxide-semiconductor FETs (MOSFETs), are a commonly used semiconductor device. Generally, a FET has three terminals, i.e., a gate structure (or gate stack), a source region, and a drain region. In some instances, the body of the semiconductor may be considered a fourth terminal. The gate stack is a structure used to control output current, i.e., flow of carriers in the channel portion of a FET, through electrical or magnetic fields. The channel portion of the substrate is the region between the source region and the drain region of a semiconductor device that becomes conductive when the semiconductor device is turned on. The source region is a doped region in the semiconductor device from which majority carriers are flowing into the channel portion. The drain region is a doped region in the semiconductor device located at the end of the channel portion, in which carriers are flowing into from the source region via the channel portion and out of the semiconductor device through the drain region. A conductive plug, or contact, is electrically coupled to each terminal. One contact is made to the source region, one contact is made to the drain region, and one contact is made to the gate stack.
A multigate device or multiple gate field-effect transistor (MuGFET) refers to a MOSFET (metal-oxide-semiconductor field-effect transistor) which incorporates more than one gate into a single device. The multiple gates may be controlled by a single gate electrode, wherein the multiple gate surfaces act electrically as a single gate, or by independent gate electrodes. A multigate device employing independent gate electrodes is sometimes called a Multiple Independent Gate Field Effect Transistor (MIGFET).